1. Field of the Invention
This invention relates to an image reproduction system which outputs a reproduction image on the basis of original image data obtained by reading out an original image recorded on a recording medium (photographic film, paper or the like).
2. Description of the Related Art
There has been put into practice in various fields an image reproduction system which outputs a reproduction image through a printer or the like on the basis of original image data obtained by reading out an original image recorded on a recording medium (photographic film, paper or the like) by the use of an image scanner or the like.
When certain kinds of phosphor are exposed to a radiation (x-rays, α-rays, β-rays, electron beams, ultraviolet rays), they store a part of energy of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is generally referred to as “a stimulable phosphor”. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as “stimulated emission”. In the medical field, there has been known a radiation image recording/reproducing system in which a stimulable phosphor sheet (a sheet provided with a layer of the stimulable phosphor) is exposed to a radiation passing through an object such as a human body to have a radiation image of the object stored on the stimulable phosphor sheet, stimulating light beam such as a laser beam is caused to scan the stimulable phosphor sheet bearing thereon the radiation image of the object, the stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light is photoelectrically detected, thereby obtaining a radiation image signal, and then a radiation image of the object is reproduced on the basis of the radiation image signal as a visible image on a recording medium such as a photographic film or a display such as a CRT. See, for instance, Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 56(1981)-11395, 55(1980)-163472, 56(1981)164645 and 55(1980)-116340.
When recording a radiation image of an object on a recording medium such as the stimulable phosphor sheet, a grid in which linear members of a radiation-untransmissible material (a material which is very low in permeability to the radiation) such as lead and linear members of a radiation-transmissible material (a material which is high in permeability to the radiation) such as aluminum or wood are alternately arranged at fine pitches of about 4/mm is sometimes interposed between the object and the stimulable phosphor sheet in order to prevent the stimulable phosphor sheet from being exposed to the radiation scattered by the object. By the use of such a grid, exposure of the stimulable phosphor sheet to the radiation scattered by the object is suppressed and the contrast of the radiation image of the object is enhanced. However, when a radiation image including therein an image of the grid is enlarged or reduced, aliasing is caused due to fold according to the rate of enlargement or reduction. Further, if the aliasing is superposed on the spatial frequency of, for instance, a grid image, fine moiré fringes are generated, which deteriorates quality of the reproduced image.
In view of these conditions, this applicant has proposed an image signal generating device which obtains an image signal, on the basis of which an image having less moire fringes and less aliasing can be reproduced, by carrying out on the image signal a filtering processing for removing spatial frequency components of the grid image (Japanese Unexamined Patent Publication No. 3(1991)-114039) and a grid removing device which extracts spatial frequency components of the grid image by the use of, for instance, Wavelet transform and removes them (Japanese Patent Application No. 2000-11174).
However, the grid removing devices such as described above for removing spatial frequency components according to the grid image generally may be installed in one of a radiation image read-out apparatus, an image processing apparatus connected downstream of a radiation image read-out apparatus and an image output apparatus (a monitor or a printer). Accordingly, when the grid removing device is installed in an image output means, it is natural that an image output from an image output means provided with a grid removing device is free from a grid image but an image output from an image output means not provided with a grid removing device cannot be free from a grid image. However, installing the grid removing device in all of the radiation image read-out apparatus, the image processing apparatus and the image output apparatus results in increase in cost and waste of the grid removing devices which are not actually used